Fuel conserving combustion gas offtake system for forced-draft furnaces



Oct. 3, 1950 L. SERAFIN] 2,524,087

FUEL CONSERVING couaus'rxon GAS OFFTAKE sysm FORFORCED DRAFT FURNACES Filed April 29, 1944 INVENTOR.

BY lu z'yl' firafini A TTORNE Y Patented Oct. 3, 1950 UNITED STATES PATENT OFFICE FUEL CONSERVING COMBUSTION GAS OFF TAKE SYSTEM FOR FORCED-DRAFT FUR- NACES Application-April 29, 1944, Serial No. 533,289

11 Claims.

This invention relates to an improvedforce draft furnace and "its leading object is to provide a furnace of this type with means for forcing the bulk of the waste products of combustion to flow from the combustion chamber of the furnace at a level well below the usual discharge to the smoke stack or chimney, which is directly over the fire pot or retort, so that the wastage of heat from the combustion chamber will be greatly reduced and the percentage of volatile elements consumed in the combustion, as well as the fuel gases generated, will be substantially increased.

In the operation of furnaces of the standard type, the waste products of combustion and considerable unconsu-med fuel, partly in gaseous and partly in fine dust condition, are caused to flow at great velocity directly into the smoke stack. This discharge carries with it a large percentage of the heat generated in combustion, and the reater the amount of heat thus wasted, the greater will be the loss of fuel to the atmosphere. I have discovered that in a forced draft furnace this wastage of heat and fuel may be diminished by forcing the products of combustion to discharge in large part at a relatively low level, and causing the balance of the products of combustion to discharge through a restricted opening through the furnace wall over the fire pot or retort.

In the normal operation of a small 'stoker fed or fired furnace, the temperature of the retort in which the fire is maintained, is so low, relative to the temperature of the fire at the point of maximum combustion intensity, that it is diflicult and often impossible to sustain combustion in the fuel bed immediately adjacent to the sides of the retort.

This naturally reduces the amount of heat generated in the retort and combustion chamber, and the cooler zone around the sides of the fire retort offers a path by which air introduced into the combustion chamber may enter the fire box or-retort, without flowing over the burning fuel.

When temperature control makes blower operationsintermittent, these cooler zones or areas duoing an undesirable cooling effect upon the structural or metal parts of the furnace and the heating system.

. part of their heat to the surfaces of the furnace result in the development of deadspots in the flue and thence to the atmosphere, without proover which they flow, before they enter the flue or overhead exhaust passage.

My system of flow also reduces the admission of excess air to the furnace, and thereby eliminates losses due to such excess.

In my fiowsystem gases of low relative temperature, and excess air admitted to the furnace, are causedto flow in a short route from the furnace, without an undesired lowering of the temperature of the surfaces of the furnace. These gases and excess masses of air are thus prevented from mixing with the gases of relatively high temperature,which rise from the fuel bed, and such hotter gases and products of combustion thus flow against the interior surfaces of the furnace at maximum effective temperatures, thereby insuring the maximum conversion of fuel into useful'heat.

The drawing shows a vertical sectional view through a forced draft furnace, constructed in accordance with my invention.

In the drawing, which illustrates one type of furnace equipped for burning solid fuel, 5 designates the retort or fire pot, which is constructed with a bell-shaped wall 6, having air feed openings Tin great number. This retort or fire pot is supplied with solid fuel or coal by means of the horizontal pipe or conduit 8, and the power driven feed screw 9 which is arranged to rotate therein, and which is adapted to force the solid fuel through the hopper-like mouth of the retort or fire pot, which opens upwardly, and provides, the usual horizontal rim [0, over which the ashes may be forced by the displacement caused by the gradual feed of the solid feed, all in accordance with standard furnace design and practice.

The fire retort or pot is enclosed by the usual conical and imper'forate shell I and the air feed conduit [2 is connected with this shell to supply air to the retort or fire pot through the openings 1, this connection being shown Well below the rim l0. -'A motor driven blower I3 maintains the supply of fresh air to the air feed conduit, all in accordance with prevailing practice.

The furnace wall 14 is of the usual water cooled or water jacket type, and includes the vertical section if: and the top horizontal section 16, to which the intake ll of the smoke stack 18 is connected. In accordance with my invention the overhead exhaust passage IQ of the horizontal furnace wall section i6 is considerably restricted, and is made with a diameter which is a minor fraction of the diameter of the intake of the smoke stack.

To provide for adequate flow of the products of combustion I arrange another exhaust passage from the combustion chamber 20, by extending a conduit or auxiliary smoke stack 2| through the vertical wall section 15, and the inner .end of this conduit is equipped with a lateral intake 22, which faces downwardly and has its open end disposed slightly above the level of the rim of the fire retort. This conduit is continued by means, of the riser 23 and communicates at its upper end with the smoke stack at a point removed from intake thereof.

I also provide a second auxiliary conduit for the waste products of combustion, indicated at 24, which extends through the vertical furnace wall section at a point slightly below the rim of the fire retort, and above the level of the air feed conduit. The inner end of this second auxiliary conduit is horizontal and normally open, and the conduit is extended to provide a vertical branch 25, which discharges into the smoke stack at a point spaced from the discharge connection of the auxiliary conduit 23.

The usual ash pit 26 is provided below the fire retort, and the usual hopper 21 is arranged around the center of the fire pot to direct the ashes centrally into the ash pit.

During combustion of the fuel supplied to the fire retort gaseous products of combustion and some combustible gases rise in great volume. Due to the restricted size of the overhead exhaust passage all of the products of combustion, and all of the combustible gases and fuel particles which rise above the zone of greatest combustion intensity cannot flow under the combined pressures of the furnace heat and the pressure of the air-feed through this restricted exhaust passage.

During the upward travel of these undischarged gases, fuel gases and fuel particles, there is a drop in their temperature. As the combined mass is subject to this drop in temperature a displacement takes place, as the continual stream from the zone of maximum combustion intensity rises in the combustion chamber, and the cooler gases and fuel particles flow downwardly against the interior surface of the vertical furnace wall section, and then are exhausted as the combustion. is continued through the auxiliary exhaust conduits, having their intakes located in the zone of relatively low temperature.

7 In this reverse flow of the unconsumed fuel gases and fuel particles, material which ordinarily exhausts before being consumed will be again exposed to higher temperatures adjacent to the fire and will be completely burned.

I have found after many successful commercial. installations that my invention results in a very material increase in the heating efiiciency of a furnace, and that fuel consumption is significantly reduced.

It is understood that liquid fuel oil may be nace having a large overhead exhaust opening, may be changed over to provide my restricted exhaust passage, by using refractory cement or other construction means, and. by constructing the auxiliary exhaust passages through the vertical wall of the furnace.

The intakes of both auxiliary exhaust conduits are located adjacent to the zone of maximum combustion intensity, but below the level of greatest heat generation, and are both near the fire retort or pot. The intake 24 and its conduit is larger in diameter and in capacity than the intake 23, and thus provides for the greatest exhaust flow immediately over the air feed conduit, which maintains a lower adjacent temperature in the furnace than is maintained adjacent to the intake of the other auxiliary exhaust conduit. This insures maximum conservation of heat units and maximum consumption of fuel.

It will thus be seen that there is provided a device in which the several objects of this invention are achieved, and which is well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in .the embodiment above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not ina limiting sense.

Having described my invention I claim:

1. In combination, a furnace providing a combustion chamber having a vertical wall section and an overhead Wall section, means spaced from at least a part of said vertical wall section for maintaining combustion in the combustion chamher, said means being located near the lower end portion'of the combustion chamber and having an outlet through which products of combustion pass to said combustion chamber, a stack for conveying the exhaust gases from the furnace, said overhead wall section having an exhaust passage from said combustion chamber communicating with said stack, said exhaust passage having a flow capacit whichis a minor fraction of the flow capacity of said stack to restrict thedischarge of exhaust gases through said exhaust passage, and at least one auxiliary conduit providing an open exhaust passage for a major portion of the products of combustion from the combustion chamber, and including one such conduit connected to said stack and to said combustion chamber at a point in said combustion chamber between said combustion maintaining means and a spaced vertical wall section of said combustion chamber and below said outlet, so that a substantial part of the products of combustion. must move downwardly in said combustion chamber to a level below that at which they were ad'mitted'to said chamber prior to passing to said stack.

2. The combination set forth in claim'l, including, means for supplyingfresh air under pressurelaterall-y into the. furnace'to the combustion maintaining means therein, the last named meansbeing located-below and adjacent to the intake of oneof said'auxilia'ry conduits for the exhaust of products of combustion from said c'om bustion chamber, so that the localized heating incident to thepassage' of products of combustion through said auxiliary conduit tends to offset localized cooling incident to said ai supplying means.

3. Incombination, a furnace. providing a combllSfiQll @hai'mber having a vertical wall section and an overhead wall section, means for maintaining combustion in the combustion chamber within the furnace, said means being located near the lower end portion of the combustion cham her, a stack for conveying the products of coinbustion from the furnace, said overhead wall section having an exhaust passage from saidcombustion chamber communicating with said stack, said exhaust passage having a flow capacity which is a minor fraction of the fiowcapacity of said stack to restrict the discharge of exhaust gases through said exhaust passage, and at least two exhaust conduits connected to said stack and connected to said combustion chamber providing open intake passages for products of combustion from said combustion chamber, said intake passages communicating with said'combustion chamber at points substantially below said exhaust passage and adjacent to the means for maintaining combustion, whereby products of combustion will flow simultaneousl through said stack and through said exhaust conduits, and means for supplying fresh air to said combustion maintaining means, the last named means being located below and adjacent to one of said intake passages which is larger than at least one other of said intake passages.

4. The combination set forth in claim 1, including means for supplying fresh air under pressure laterally into the furnace and located below and adjacent to one of the exhaust intakes from said combustion chamber for one of said auxiliary conduits, and another exhaust intake from said combustion chamber for another of said auxiliary conduits having a vertical branch in said chamber opening downwardly thereinto.

5. In combination, a furnace providing a combustion chamber having a vertical wall section and an overhead wall section, means'for maintaining combustion in the combustion chamber within the furnace, said means being located near the lower end portion of the combustion chamber, a stack for conveying the products of combustion from the furnace, said overhead wall section having an exhaust passage from said combustion chamber communicating with said stack, said exhaust passage having a; flow capacity which is a minor fractionof thelfiow capacity of said stack to restrict the discharge of exhaust gases through said exhaust passage, and at least two exhaust conduits connected to said stack and connected to said combustion chamber providing and an overhead wall section, means for maintaining combustion in the combustion chamber within the furnace, said means being located near the lower end portion of the combustion chamber, a stack for conveying the products of combustion from the furnace, said overhead wall section having an exhaust passage from said combustion chamber communicating with said stack, said exhaust passage having a flow capacity which is a-minor fraction of the flow capacity of said stack to restrict the discharge of exhaust gases through said exhaust passage, and at least two exhaust conduits connected to said stack and connected to said combustion chamber providing open intake passages for products of combustion from said combustion chamber, said intake passages communicating with said combustion chamber at points substantially below said exhaust passage and adjacent to the means for maintaining combustion, whereby products of combustion will flow simultaneously through said stack and through said exhaust conduits, one of the intake passages for products of combustion from said combustionchamber having a vertical branch located in said combustion chamber and facing downwardly therein, and another intake passage for products of combustion from said combustion chamber having a horizontall disposed opening and being located at a, lower level than the first named intake passage.

7. The combination set forth in claim 1, including means for supplying fresh air under pressure laterally into the furnace located near the lower end of said combustion chamber and below and adjacent to the point at which one of said auxiliary conduits communicates with said combustion chamber, so that the localized cooling incident to the means for supplying fresh air to the combustion chamber will be offset at least in part by 'the localized heating incident to the adjacent exhaust intake to said one auxiliary conduit, said exhaust intake having a horizontally disposed opening, and another exhaust intake for another of said auxiliary conduits having its end communicating with the combustion chamber at a slightly higher level and having a verv tical branch within said combustion chamber which is normally open and faces downwardly.

8. A forced draft furnace having a combustion chamber defined by side and top walls, means for burning fuel in the lower portion of said combustion chamber including means for supplying combustion-supporting air under pressure to the fuel burning means, said fuel burning means having an outlet through which products of combustion pass to said combustion chamber, which outlet is spaced laterally from at least a part of a side wall of said combustion chamber, a stack, means providing a passage between the upper portion of said combustion chamber and said stack of such restricted area that only a minor portion of the gaseous products of combustion can flow therethrough to the stack, and means providing at least One passage of relativel greater total cross sectional area than the first named passage, communicating with said combustion chamber at a level substantially below the first named passage and below said outlet andwith said stack for conducting the major portion of the products of combustion from the combustion chamber, so that a substantial part of the products of combustion must move downwardly in said combustion chamber to a level below that at which they were admitted to said chamber prior to passing to said stack.

9.. A forced draft furnace having a, combustion chamber defined by side and top walls, means located centrally of the combustion chamber at the lower portion thereof and spaced from said side walls for burning fuel therein, including means for supplying combustion-supporting air under pressure to the fuel burning means, said fuel burning means having an outlet through which products of combustion pass to said combustion chamber, a stack, means providing a passage between the upper portion of said combustion chamber and said stack of such restricted area that only a minor portion of the gaseous product of combustion can flow therethrough to the stack, and means providing at least one passage of relatively greater total cross sectional area than the first named passage, communicating with said combustion chamber laterally intermediate the fuel burning means and said side walls and at a level substantially below the first named passage and below said outlet and with said stack for conducting the major portion of the products of combustion from the combustion chamber, so that a substantial part of the products of combustion must move downwardly in said combustion chamber to a level below that at which they were admitted to said chamber prior to passing to said stack.

10. A forced draft furnace having a combustion chamber defined by side and top walls, at least a major portion of said side walls being externally water-cooled, means for burning fuel in the lower portion of said combustion chamber including means for supplying combustion-supporting air under pressure to the fuel burning means, said fuel burning means having an outlet through whichproducts of combustion pass to said combustion chamber, which outlet is spaced laterally from at least a part of a side wall of said combustion chamber, a stack, means providing a passage between the upper portion of said combustion chamber and said stack of such restricted area that only a minor portion of the gaseous products of combustion can flow therethrough to the stack, andmeans providing at least one passage of relatively greater total cross sectional area than the first named passage communicating with said combustion chamber at a level substantially below the first named passage and below said outlet and with said stack for conducting the major portion of the products of combustion from the combustion chamber, whereby the action of the said outlet passages in conjunction with that of said water-cooled side walls is effective to produce circulatory currents of gases in said combustion chamber upwardly in the center portion thereof and downwardly adjacent to said side walls, so that a substantial part of the products of combustion must move downwardly in said combustion chamber to a level below that at which they were admitted to said chamber prior to passing to said stack.

11. A forced draft furnace, comprising a substantially cylindrical combustion chamber wherein the axis of said cylinder is vertical and defined 8 i by water cooled top and side walls, means in the lower central portion of said combustion chamber spaced from said side walls for burning comminuted solid fuel including means for supplying combustion-supporting air under pressure to the fuel burning means, said fuel burning means having an outlet through which products of combustion pass to said combustion chamber, a stack, means providing a passage through the central portion of the top wall of said combustion chamber communicating between the inside of said combustion chamber and said stack and of such restricted area that only a minor portion of the products of combustion can flow therethrough to the stack, and separate and distinct means providing a plurality of passages communicating between the lower lateral portions of said combustion chamber at a level substantially below the first named passage and adjacent to that at which the fuel is burned and with said stack for conducting a major portion of the products of combustion from the portion of said combustion chamber intermediate said fuel burning means and the side walls thereof, at least one of said pluralityof passages having its entrance opening to the interior of said combustion chamber located at a level below said outlet, said last named passages being of relatively greater total cross sectional area than said first named passage for conducting a major portion of the products of combustion from said combustion chamber to said stack, the first named passage and the watercooled side walls mutually coacting with the centrally located fuel burning means to create circulatory currents of products of combustion in the combustion chamber upwardly at the center portion thereof and downwardy adjacent to said side walls, so that a substantial part of the products of combustion must move downwardly in said combustion chamber to a level below that at which they were admitted to said chamber prior to passing to said stack.

LUIGI SERAFINI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 58,164 Chase Sept. 18, 1866 64,540 Kafer et al. H May 7, 1867 2,122,733 Van Rijswijk July 5, 1938 2,170,277 Richardson Aug. 22, 1939 2,342,272 Hayter Feb. 22, 1944 

